Global Alert and Response (GAR)

Pandemic (H1N1) 2009 - update 74

Weekly update (Virological surveillance data)

The Global Influenza Surveillance Network (GISN) continues monitoring the global circulation of influenza viruses, including pandemic, seasonal and other influenza viruses infecting, or with the potential to infect, humans including seasonal influenza.

  • Globally, since the beginning of the pandemic 19 April to October 31st 2009, a total of 81 countries reported to FluNet. The total number of specimens reportedly positive for influenza viruses by NIC laboratories was 195,005. Of these, 126,888 (65.1%) were pandemic H1N1, 7049 (3.6%) were seasonal A (H1), 20,720 (10.6%) were A (H3), 35,381 (18.1%) were A (not sub typed) and 4967 (2.5%) were influenza B.
  • For this reporting week (25 October to 31 October 2009); a total of 32 countries reported to FluNet. The total number of specimens reportedly positive for influenza viruses by NIC laboratories was 15,634. Of these, 12,329 (78.9%) were pandemic H1N1, 85 (0.5%) were seasonal A (H1), 203 (1.3%) were A (H3), 2920 (18.7%) were A (not subtyped), 97 (0.6%) were influenza B.
  • Detailed virological information for the European Region of WHO is included in the EuroFlu Weekly Electronic Bulletin (see link below)
  • The majority of all influenza detections were reported by the United States of America followed by China and Norway. Among the 32 countries reported to FluNet, on average, the pandemic A (H1N1) accounted for 78.8% of all flu detections for the northern hemisphere (30 reporting countries) and (100%; 4/4) for southern hemisphere (2 reporting countries).
  • The above numbers represent only the specimens and results reported to FluNet. Some laboratories (NICs), under pressure of the pandemic surge, do not test for seasonal subtypes and accordingly, this data should be interpreted with caution.

Systematic surveillance conducted by the Global Influenza Surveillance Network (GISN) including WHO Collaborating Centres (WHOCCs) for reference and research on influenza, continues to detect sporadic incidents of H1N1 pandemic viruses that show resistance to the antiviral oseltamivir. To date, 52 oseltamivir resistant pandemic H1N1 influenza viruses have been detected and characterized worldwide. All of these viruses show the same H275Y mutation. All these viruses remain sensitive to zanamivir. Worldwide, more than 10,000 clinical specimens (samples and isolates) of the pandemic H1N1 virus have been tested and found to be sensitive to oseltamivir.

All pandemic H1N1 2009 influenza viruses analysed to date were antigenically and genetically closely related to the vaccine virus A/California/7/2009.

Virology data update

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